Enables software tag-based KASAN mode.

This mode require software memory tagging support in the form of
HWASan-like compiler instrumentation.

Currently this mode is only implemented for arm64 CPUs and relies on
Top Byte Ignore. This mode requires Clang.

This mode consumes about 1/16th of available memory at kernel start
and introduces an overhead of ~20% for the rest of the allocations.
This mode may potentially introduce problems relating to pointer
casting and comparison, as it embeds tags into the top byte of each
pointer.

Currently CONFIG_KASAN_SW_TAGS doesn't work with CONFIG_DEBUG_SLAB
(the resulting kernel does not boot).

source code:

mm/kasan/